* Implement `/dnsaddr` support on `libp2p-dns`.
To that end, since resolving `/dnsaddr` addresses needs
"fully qualified" multiaddresses when dialing, i.e. those
that end with the `/p2p/...` protocol, we make sure that
dialing always uses such fully qualified addresses by
appending the `/p2p` protocol as necessary. As a side-effect,
this adds support for dialing peers via "fully qualified"
addresses, as an alternative to using a `PeerId` together
with a `Multiaddr` with or without the `/p2p` protocol.
* Adapt libp2p-relay.
* Update versions, changelogs and small cleanups.
Move transport upgrade protocols from `protocols/`
to `transports/`, such that only "application protocols"
that depend on `libp2p-swarm` remain in `protocols/`,
whereas there is no such dependency in `transports/`
outside of integration tests.
Tweak README and top-level CHANGELOG.
